.nav-header{
     position: fixed;
     left:0;
     top:0;
     height:100px;
     z-index: 1000;
     width:100%;
     box-sizing: border-box;
     text-align: center;
     line-height: 100px;
     background-color: #2A2A2A;
     color:#FFF;
     i{
         position: absolute;
         left:20px;
         line-height: 100px;
     }
}